This application claims priority to EP/01107385.5, filed Mar. 26, 2001 under the European Patent Convention and which is incorporated by reference herein in its entirety.
The present invention relates to a turbine blade or vane, in particular for a gas turbine, which has at least one chamber which can be acted on by a cooling medium and, at a rear edge, has a gap, which is delimited by two walls, for the cooling medium to be discharged. It also relates to a process for producing a turbine blade or vane of this type.
A turbine blade or vane of this type and process for its production are known, for example, from U.S. Pat. No. 5,419,039 and WO 99/59748. The turbine blades or vanes are generally produced using a casting process. To do this, in many cases one or more cores made from a ceramic material are produced and are then embedded in a wax mold. After casting with the desired material for the turbine blade or vane, the core or cores is/are removed, in particular by leaching. On account of shrinkage factors on the part of the cores, the wax, an outer core shell and the material used for the turbine blade or vane, it is impossible to achieve especially high levels of accuracy for the gap at the rear edge.
However, this gap is crucial to the way in which the cooling medium is applied to the turbine blade or vane. If the cross section of the gap is too small, the flow of cooling medium is insufficient, so that the turbine blade or vane is no longer sufficiently cooled. There is then a risk of the turbine blade or vane failing when used at high temperatures.
To ensure that the gap still has the required minimum cross section taking account of all the factors of influence, it is therefore necessary to assume a relatively high tolerance. This means that many of the turbine blades or vanes which are produced have a gap cross section which is larger than the minimum acceptable gap cross section. Accordingly, these turbine blades or vanes have a relatively high flow rate of cooling medium and are therefore cooled to an unnecessary degree. This leads to a deterioration in the efficiency, since the cooling medium in many cases has to be taken from a compressor, which is driven by the turbine, at relatively high pressure.
Therefore, it is an object of the present invention to provide a turbine blade or vane which, while being simple to produce, allows the consumption of cooling medium to be minimized. A further object of the invention is to provide a process for producing a turbine blade or vane of this type.
According to the invention, this object is achieved, in a turbine blade or vane of the type described in the introduction, by the fact that at least one of the walls can be remachined in order to change the cross section of the gap. In the process according to the invention, it is provided that the rear edge of the turbine blade or vane is remachined so as to change a length of at least one of the walls, in order to change the cross section of the gap.
Unlike with the known turbine blades or vanes and production processes, for the first time the cross section of the gap can be changed in a controlled manner. This change is achieved by changing the length at least one of the walls which delimit the gap. The result, accordingly, is a change in the cross section of the gap, so that the flow of cooling medium through the gap can be varied.
According to the invention, therefore, it is now possible to provide turbine blades or vanes which have a gap cross section which is favorable for production. This cross section is adapted to the respectively prevailing boundary conditions by remachining of the walls which delimit the gap in order to optimize the flow of cooling medium. The cross section of the gap is increased or reduced in size by remachining, depending on the way in which these walls are arranged with respect to one another. The previous need to design so as to achieve the minimum required gap cross section during production can be eliminated.
Advantageous configurations and refinements of the invention will emerge from the dependent claims.
In the blade or vane according to the invention, the cross section of the gap can advantageously be changed by changing the length of at least one of the walls. In particular, the pressure-side wall may be remachined. According to an advantageous configuration, the machining is carried out using an erosion process. The length of the walls can be measured without problems. A change with a high level of accuracy and therefore optimum setting of the cross section of the gap is possible.
According to a first advantageous configuration, at least one of the walls is provided with shoulders which project into the gap and can be changed by the remachining. The result is a corresponding change in the cross section of the gap. Alternatively, the gap may be of substantially constant thickness, which can varied by the remachining.
Therefore, in the region of the gap the walls may be arranged at an angle or substantially parallel to one another. When walls arranged parallel to one another are used, the cross section is changed using the shoulders. These shoulders have a cross section which differs in the longitudinal direction of the walls. Therefore, when the length is changed, the cross section of the shoulders changes automatically, and therefore so does the cross section of the gap.
If the walls are arranged at an angle to one another, it is possible to change the cross section of the gap even without these shoulders being required. However, it is obviously also possible for the shoulders to be provided on angled walls as well.
In the process according to the invention, after the turbine blade or vane has been produced the cross section of the gap is advantageously determined and then the remachining is carried out as a function of predeterminable boundary conditions. Therefore, it is possible for each individual turbine blade or vane to be specifically optimized. As a result, the consumption of cooling medium can be reduced considerably.
The cross section can either be measured directly, for example using optical methods, or may be measured indirectly by measuring the flow of cooling medium through the gap. It is also possible to measure the supply of cooling medium to the turbine blade or vane, this supply being dependent on the flow through the gap. Then, if necessary, remachining is carried out on the basis of the measured flow rate or the measured supply and the desired flow rate. To increase the accuracy, the cross section may be redetermined, if appropriate followed by further remachining.